Looking for some thoughts on an intermittent issue that I have with the trip pump on my boat.

I have twin Mercury 525EFIs and bravo XR drives. On my boat I have a single switch in my throttle to control the up/down trim for both drives, as well as individual port/stbd trim switches on my dash and also a transom mounted individual port/stbd switch set.

I have noticed that when I have been running the boat for a while and then let it sit for a few hours while anchored/etc, that sometimes I will not be able to trim down on one or both drives using the switch in the throttle or the dash switches, however the transom mounted switches work fine.

When it's not working, I see the battery voltage in my gauge drop when I engage the switch which makes me think that the switch is working OK. When the boat has been sitting the garage for a while everything works great which makes me suspect that something could be failing when it gets warmed up in the engine compartment.

I need to look at my wiring, but does anyone know if there could be something different about how the transom switch is wired in vs the throttle/dash switches? If all of the wiring from the dash and transom switches go to the same place, could it be as simple as a failing solenoid on the trim pumps? It seem like an unlucky coincidence to have this happen on both trim pumps at the same time and also I don't understand why the transom switch works just fine but not the dash switches.

Any ideas for me to check when I'm looking at it?

If the switches on the transom work each and every time then it rules out the pump itself or the solenoids....i would concentrate on the wiring...probably where it connects the throttle switches with the dash switches.
If you have a single switch in the throttles to do both drives then there are diodes wired in to keep the circuits from back feeding when using the dash switches....maybe one/both are going bad and shorting out when they get hot??

chek this out on the last page

Thanks for the feedback! The transom switch seems to work every time, so I know that the pump is good. I haven't checked, but if there is only one solenoid then it would make me think that the solenoid is also OK since it goes to the transom switch and the dash switches.

I do have the diodes that you mentioned to ensure that the circuit doesn't back feed when the dash switches are used as you mentioned. I am think that if I disconnect the diodes and the throttle switch, then I could at least test out the wiring from the dash back to the pump if the dash switches work fine (obviously I would not have the throttle switch functionality while doing this testing).

The part that stumps me is that it's intermittent but also fairly reliable for when it stops working. If the boat has been sitting for a day or so then everything work fine, but after a day on the water after sitting for a few hours, it almost always stops working which makes me wonder if there is something heat related back in the engine compartment.

The solenoids are mounted right at the pumps....so if the pumps are working up/down then solenoids are good to go......maybe your confusing them for relays if mounted somewhere other then right on the pump assemblies???

Thanks - I didn't really word my response very well. It looks like each of my trim pumps has one set of solenoids mounted at the pumps (one for up/one for down), but I'm not sure if the wiring from the switches goes directly to the pumps or if there is a relay before the pumps. I guess I need to spend some time tracing the wiring to see where it goes.

Can you think of any reason why the failure would not be consistent? If it was "broken" the entire time it would be easier to diagnose for sure.

I would venture to guess....and its a BIG guess here...but i think its a wiring connection of the Green and Blue wires at the dash causing the issues. If you look at a schematic of the power trim system...the trim pump has the power and ground hooked directly at the pump...then you will have 3 wires going up the the dash. A Red (Power) a Green (Down) and Blue (Up)
And each pump/switch combo would have its own set of wires running up to the dash. (Its the same for the trim tabs if you have merc k-planes as well)
So if both drives are non-operational at the very same time, And being that they each have their own power circuit, then to my mind its got to be the connection where the throttle switches are spliced into the mix that is causing the issues. My guess is the diodes are going bad and shorting out the system.....why its happening later and not when cold i cant guess on...maybe you running the drives down at the start heats up the diodes and then they fail? It would be interesting to go out there when its all cold and run the drives up and down fully a few times and see if they quit working after 1-2 cycles.... if they do then i would replace diodes...if not then you have to start testing the wiring and checking the connections along all the contact points...

I just re-read your original response again.

Yes I have the diodes wired in with the single throttle switch and dual dash switches. I had a problem with one of the diodes that had shorted out a couple of years ago and 1 of the 4 diodes was replaced. Perhaps this is where my issue is.

I think my next step is to remove all of the diodes and also disconnect the throttle switch from the wiring. This way I will only have the dash switches wired and this removes the possibility of something with the diodes or throttle switch causing the issue, correct?

That would work and an easy way to help narrow things down a bit